Process for separation of gasoline fractions of different octane number by cyclic adsorption



y 7, 1 5 R. J. HENGSTEBECK ETAL 2,893,944

PROCESS FOR SEPARATION OF GASOLINE FRACTIONS OF DIFFERENT OCTANE NUMBER BY CYCLIC ADSORPTION Filed April 19, 1955 Wet Gas fSTAB/l. IZER TOWER Raw Refarmate I /0 wow/Pam COOL El? \/9 25 l High Octane 22 28 r Intermediate Octane Low Octane IN V EN TORS:

m ggz/n ATTORNEY PROCEEiS 0R EsEPARATIGN 0F GASOLINE C- TKQNS @F DEFFERENT QCTANIE NUMBER Y (:YCLHC ADSORPTEQN Robert .l'. Hengsteheclr, Valparaiso, and Joseph E. Wolf, Munster, Ind, assignors to Standard Oil Company, Chicago, lllh, a corporation of Indiana Application April 19, 1955, Serial No. 502,393

14 Claims. (Cl. 203-=-95) This invention relates to improvements in the production of high octane gasoline, particularly where more than one octane grade of gasoline is produced, by procedures including a reforming operation. In a more specific aspect, the invention relates to an improvement in catalytic reforming whereby production of more than one octane number product is provided by a relatively simple and inexpensive segregation process.

In order to meet the high octane levels prevailing currently and the higher levels projected for the future, the modern refiner must use a process such as catalytic reforming for up-grading low octane naphthas, in addition to conventional cracking, fractionating and blending operations. Although reforming, particularly catalytic reforming in the presence of hydrogen, is an effective way to increase the octane level of virgin or other low octane stocks, the upgrading is done at the expense of total gasoline since the chemical conversions involved produce dry gas and coke, while the production of aromatics and isoparafiins from parafiins inherently results in volume reduction. Hence, the refiner tries to conduct reforming under the mildest conditions that permit attaining the minimum octane number specified for the refinery gasoline pool.

It may be impossible, however, to operate in this economically desirable manner unless the relative proportions of premium and regular, or lower octane grades of gasoline, required by the pool are in balance. For example, as sales of premium gasoline are increased, the refiner may find it impossible to meet the prevailing premium octane level with the blending stocks available, i.e. reformate, catalytically cracked gasoline, straight run gasoline fractions, polymer gasoline, and special blending agents such as alkylates, butane, isopentane, etc. and tetraethyl lead. Then, it is necessary to increase the severity of the reforming operation beyond that required to meet the over-all octane requirement for the refinery gasoline pool, or introduce some form of reformate fractionation which will provide selectively a higher octane reformate for blending premium gasoline.

Either expedient is costly. Increased reforming severity is expensive in terms of increased loss of charge stock to gas and coke. Also, as the inherent and design limitations on the octane level attainable with the given reforming process are approached, other disadvantages appear. Yield losses increase when optimum severity is exceeded because of decline in selectivity. Also, deactivation of the catalyst and coke lay-down are accelerated, necessitating more frequent regeneration. Over-all life of the catalyst may be seriously reduced.

On the other hand, conventional fractionation of the reformate product to recover a selected fraction of higher octane number than that of the whole reformate cut is costly because the hydrocarbon types requiring separation are close boilers. Super-fractionation equipment must be installed. Thus, both capital investment and operating expenses may be increased disproportionately to the benefit obtained. Similarly, use of selective solvent extraction, or extractive distillation, is expensive in requiring special facilities for handling and stripping solvent, etc.

The present invention provides a relatively simple and inexpensive procedure for segregating reformate selectively into high octane, intermediate octane (corresponding to the average octane of the reformate itself) and low octane fractions. According to the invention, reformate is subjected to a cyclic aromatics adsorption-aromatics stripping process conducted at differential temperatures. The process involves a four-phase cycle operating on a typical reformate stream. In the first phase, the reformate is passed through an adsorption Zone in contact with a solid particle-form, adsorbent, selective for aromatics, for a period of time sufiicient to substantially saturate the adsorbent. As selective saturation of the adsorbent, e.g. silica gel, develops, the adsorbate is enriched in aromatics while the efiluent becomes leaner in aromatics. Thus, the octane number of the efiluent reformate declines. Before saturation of the adsorbent is completed, the temperature of the reformate passing to the adsorption Zone is adjusted to an elevated temperature whereby continued flow of the reformate stream acts to purge the adsorbent bed of low temperature reformate hydrocarbons. The efiluent from the adsorption zone is segregated so that the low octane product of the first phase of operation and the intermediate octane product of the second phase of operation are collected separately. After the adsorbent is purged of low temperature hydrocarbons, aromatics adsorbed thereon are stripped from the adsorbent by continuing the flow of reformate to the adsorption zone at elevated temperature favoring desorption. Thus, during this phase of the operation, a high octane product, rich in aromatics, is produced. To complete the cycle, the adsorbent is purged of high temperature reformate hydrocarbons, as the stripping operation approaches completion, by adjusting the temperature of the reformate feed to the level desired for aromatics adsorption. The product during this phase is an intermediate octane product, corresponding to that of the reformate feed. The cycle is then repeated.

Advantageously, the reformate charged to the adsorption-stripping cycle is withdrawn from the reforming operation, after conventional removal of recycle hydrogen gas by flashing and, if desired, after conventional stabili zation to remove light hydrocarbon gases. Ordinarily, the reformate is at a temperature in the range of about 350 to 550 F., which is particularly satisfactory for the operation of the invention. The reformate at the available temperature, say about 450 F., is used in the high temperature purge and stripping phases of the cycle. For the saturating and low temperature purging phases of the cycle, the reformate flowing to the adsorber is cooled to as low a temperature as is practicable with ordinary refinery cooling facilities, say about F.

Three product streams of dilferent octane level are produced by the selective segregation system of the invention although the system can be operated, if desired, with less selectivity by separating the adsorber effluent into two outs of relatively high and relatively low octane. Advantageously, the high octane fraction is blended to premium gasoline with other premium blending stocks such as catalytic or polymer gasoline alkylate and the like. The intermediate octane fraction, corresponding to the octane level of the reformate as produced, may be blended to regular gasoline, or may be partially blended to premium and partially to regular gasoline. The low octane fraction may be blended to regular gasoline if the average octane number of the over-all pool permits, or to a lower grade gasoline. Also, in another aspect of the invention, it may be recycled to the reforming reaction. Since it has ben selectively enriched in paraffins and 'naphthenes, it may be profitably upgraded by rerunning in the reforming operation, either as recycle or, more selectively, ill a separate second pass operation.

The segregation system of the invention has substantial advantages in simplicity of operation and savings in equipment and operating expense compared to other fractionation systems. It requires only a single adsorber drum or tower (although more than one may be used if desired) and simple heat exchange equipment, plus appropriate fittings for pumping the products to segregation storage or recycle. The expensive distillation or extraction towers, heaters, condensers, solvent stripping and handling facilities of conventional fiactional distillation or solvent extractive methods are unnecessary. Also, unlike selective adsorption as conventionally proposed for aromatics recovery, there is no need to provide a multiplicity of adsorber towers, with complex valving for shifting from one adsorber to another to maintain on-stream continuity, or facilities for conductingregeneration and for handling regeneration fluids.

Referring now to the diagrammatic flow plan representedin the accompanying drawing, the invention will be described in greater detail.

' In the drawing, raw reformate from a typical catalytic reforming process, for example, a fixed bed catalytic hydroforming process using a platinum-alumina catalyst or a fluidized molybdenum-alumina hydroforming process, flows via line to stabilizer tower 11. Usually, the raw reformate stream in line 10 will be at a moderately elevated temperature in the range of about 250 to 500 F., and at elevated pressure. Stabilizer tower 11 may be operated by withdrawing a liquid stream from a lower tray of the tower and pumping it through steam reboiler 12 before recirculation to the tower. The tower overhead passes from line 13 through cooler 14 into receiving drum 15. The uncondensed gas stream vents from drum 15 through line 16. Reflux liquid is returned to the tower top by means of connection 17.

The stabilized reformate is removed from the bottom of tower 11 by means of connection 18. According to the invention, it then may be passed through valved line 19 to adsorber inlet line 20, and thence to adsorber 21. The stabilized reformate is so handled, at the bottoms temperature of tower 11, during the high temperature purge and stripping phases of the operating cycle. During the adsorption or saturating phase and the low temperature purge phase, the reformate from tower 11 and bottoms line 18 is passed by means of valved line 22 through cooler 23 before introduction to adsorber inlet line 20.

Following passage through the silica gel bed of adsorber 21, the reformate is passed by means of line 24 through cooler 25, and, via one of valved connections 26, 27 and 28, to storage or recycle. During the adsorption or saturating phase of the cycle, the reformate from adsorber bed 21 is withdrawn as low octane product through line 26, advantageously for recycle to the reforming operation, or alternatively to stora'ge. During the two purging phases of the'cycle, the reformate from adsorber 21 is withdrawn as an intermediate octane prodnot through valved line 27. During the aromatic stripping phase of the cycle, a high octane fraction is withdrawn to tankage, or to a'continuous blending'operation via valved line 28.

In an example of operation according to the invena a '4 tion, raw reformate (54.6 API) is charged at the rate of 8,156 barrels per stream per day to stabilizer tower 11 at a temperature of 320 F. The stabilizer tower 11 is operated under depropanization conditions with a temperature of 120 F. at the tower top. The overhead is condsensed at F., and 245 p.s.i.g. Wet gas at the rate of 2,483 pounds per hour is withdrawn from the system. The bottoms temperature of 430 F., at 260 p.s.i.g., is maintained by recirculating a liquid stream at 395 F., through steam reboiler 12.

The stabilized gasoline stream (51.8 API) is charged to adsorber bed 21 at the rate of 7,802 barrels per day. The octane number of the stabilized reformate is 77.5 CFR-R clear. The silica gel used has an apparent density of 0.7, or 43 pounds per cubic foot, and an actual particle density of 2.2, or 137 pounds per cubic foot. There is in effect 0.314 cubic foot of gel per cubic foot of adsorber volume.

Sizing the adsorber is a matter of practical economics rather that a controlling process variable. The larger the contact mass, i.e., the adsorber drum, the wider is the split eifected between high and low octane fractions. With a half-hour cycle for saturation and another halfhour period for desorption and a space velocity of 0.191- gallon of reformate per pound of silica gel per hour, 36,800 pounds of silica gel are used in adsorber 21. An adsorber vessel approximately 7 x 22 is used.

The silica gel bed holds about 4260 gallons of liquid and about 2040 gallons are required to heat the bed from 100 F. to 430 F., the temperature of the reformate charge. 1 In a typical cycle (any cycle after the first), assume that the liquid is leaving the bed at 430 F. and that the efliuent octane is just past the peak of the cycle and is falling to low octane. The reformate charge is passedthrough cooler 23, and the 100 F. reformate is charged to adsorber 21 for 4790 gallons. The charge is now switched to 430 F. liquid for 6830 gallons. Finally, 2040 gallons of 100 F. liquid are charged to complete the cycle.

During the cycle, the effluent will be at 430 F. for

4260 gallons. It will be at 100 F. for 6830 gallons.

It will be at 430 F. again for 2570 gallons. The data on the complete cycle are summarized in the following table.

Low Int. High Octane Octane Octane No. N o No.

It will be seen by plotting eflluent octane number against the volume of reformate charged that the cycle approximates a sinusoidal curve in appearance which may be related in cycle time to the temperature cut points. Optimum operation calls for an overlap between thetiming of the temperature switching cycle and the timing of the octane switching cycle. In controlling the operation, both temperature and octane (usually by refractive index) are followed, andthe inlet temperature is switched in antici-' pation of complete gel adsorption'or desorption as the case may be in order to allow for the hold-up of liquid inthe bed and the resulting lag at the outlet end in reflecting the changed operating condition.

v The efiluent octane numbers can be followed readily and continuously by means of instruments such as recording refractometers or density meters or hydrogen to carbon ratio meters, without waiting for actual octanenumber determination. As noted above, there is a necessary overlap between the functional phases of the operating cycle and thetemperature cut-points. For convenience, it is desirable to time the shift from low to high temperature before complete saturation and from high to low temperature before complete stripping, taking into account bed size, volumetric hold up in the bed and space velocity. Once the system is lined out, operating experience coupled with instrumentation of the type indicated above provide adequate controls. The actual octane differentials obtained may be varied considerably, and this again represents an economic question, taking into account the over-all refinery situation.

The above operating example is based upon experimental data obtained in runs using a steel flow reactor, containing a bed of silica gel and a preheat section filled with glass beads. The steel reactor tube was 4' long and about inside diameter. The entire reactor tube was surrounded by an insulated heating jacket. The heating jacket was divided into an upper heater and a lower heater. A double, circular, stainless steel, fine wire-mesh screen was used to support the silica gel bed. The two screens contained a layer of glass wool between to help support the gel. The wire screen and silica gel was supported by a perforated metal disk attached to the thermowell of the reactor which extended up the middle of the reactor tube.

Two thermocouples were inserted in the thermowell and placed at the middle of the silica gel bed and the middle of the upper preheat section. The reactor tube was filled with 60-20O mesh silica gel until the top of the silica gel bed coincided with the bottom of the upper heater. The preheat section was filled with glass beads. The reactor tube containing the silica gel was attached to the unit and the system was flushed with nitrogen gas. The feed was pumped downflow from a Hills-McCanna pump. The effluent passed through a steel condenser tube cooled by water and into a steel receiver. The efiluent was drained into a round bottom flask containing a Dry-Ice knock-back. The sample was drawn from the bottom of the flask by means of a stop-cock.

The feed was a hydroformate from a fluid type molyb- 6 tional runs were made at 500 to 700 p.s.i.g., obtained by nitrogen pressuring, to keep the charge liquid at the elevated temperatures employed. The weight of silica gel in the bed was 82.7 grams.

Space velocity data comparing cubic centimeters of feed or efliuent per gram of silica gel per hour, indicated a significant increase in elfluent rate during desorption at atmospheric pressure. Apparently, a vaporization of the hydrocarbon stream in the silica gel bed left a relatively dry silica gel bed which was highly activated for adsorption. Consequently, the pressure runs appear to give a somewhat lower octane number stream in high yield than the runs at atmospheric pressure.

Flow data on the two types of runs are tabulated below in Table I. Analytical data of composite samples taken during the two types of runs are tabulated in Table II below. The composite samples reported are representative of average differences in octane number for the high and low octane cuts over the course of the runs and do not reflect the octane differential between the richest and leanest cuts observed for the efiluent. In the runs at atmospheric pressure, the octane numbers between the aromatic-rich and the aromatic-lean streams differed by as much as 19.6 units with 37.1% of the effluent having an octane number 6.3 units higher than the feed. In the run made under 500 p.s.i.g pressure, the aromatic-rich and aromatic-lean streams differed in octane number by as much as 14.1 units with 3.5% of the elfluent having an octane number 6.2 units above the feed. In addition the pressure run gave 20.4% eifluent with an octane number 2.0 units above the feed.

In all of the runs, the first low octane stream obtained from saturating the silica gel with feed was discarded. The temperature dilferential in both types of runs ranged from about 80 F. during the low temperature input phases to about 500-550 F. during the high temperature input phases. The fiow and analytical data follow:

Table I dena-alumina hydroforming unit, produced in \a pilot plant using a commercially available catalyst at moder- P Feed Effluent ate conditions. The feed to the fluid hydro-former was Run Cycle f igf" kg, a mixture of M1d-Cont1nent, West Texas v1rg1n and West e/cl (c L/ Texas coke still naphthas, having an initial boiling point r) r) of 118 F.; 268 F.; and a maximum of 484 F. saturate Atmos 189 1 41 It contained 41% aromatics, 3% olefines and 56% par- 03,0101 555:1: Atmosj 2 afiins and naphthenes and had an octane number of 77.3 ycle I (c0ld) Atmos 71 3% Research, clear. 1155 1131 In the first run, which was made at atmospheric pres- 50 2; i3; sure, the bed comprising 71.7 grams of silica gel was Cycle IV (hot) Atmosi 1159 2152 saturated with feed until the refractive index of the gj g2 efiluent reached that of the feed. Initially, the upper pre- 8yole 115 5 1I go 1133 4 ye e co 0 1. 4 0.85 heat section of the reactor only was heated to preheat Cycle 11 (hot). 680 1.30 1.10 the feed. Because of heat losses 1n the small bed, it was 55 015 glugh?) egg 1. 4 1. ye e o 5 0.9 0. found necessary to heat both the preheat section and the cycle In (COMLU 605 0. 50 (L 48 s1l1ca gel sectlon by means of the heatlng acket in orgyele 5110 2;--- gag 8.3; 8.2;

yc e 00 der to obtain elfectlve desorptlon of aromatics and act1- Cycle, 010mm 535 M4 0'61 vation of the s1l1ca gel. ycl V 4 5 0-9 0-75 Following several atmospheric pressure runs, addi- Table II Refractive Para-inns Octane Composite Index and N aph- Olefins, Aromatics, Efliuent, No

Sample N 20/D thenes, Percent Percent Percent OFR-R Percent (Clear) Feed 1. 4448 66.0 a. 0 41. 0 77. a 7-74A-L 1. 4321 68.0 3. 5 2s. 5 12. 4 e5. 8 7-74A-L2 1. 4429 57.0 3. 5 a0. 5 14. 3 77. 7 774A-R 1. 4575 44.5 2. 5 5a. 0 23.1 85. 4 7-74A-R2- 1. 4524 50.0 a. 0 47. 0 14.0 81.0 781AR 1. 4554 47. 0 a. 0 50.0 15.1 84. 4 7-8lA-R2. 1. 4534 50. 5 a. 0 45. 5 16. 4 82.6 7-81AR3 1. 4489 53. 5 3. 0 4a. 5 20. 4 79. s 781AL 1. 4332 55. 5 3. 5 30. 0 11.2 70. 3 7-81A-L2 1. 4419 1o. 6 75. 5

Hence, this invention provides means for splitting reformate into high and low octane fractions by a simple continuously operated segregation system. The production of increased quantities of premium gasoline is facilitated in an economical manner without needlessly relieve process'severity and by selective recycle of low octane components, whereby production of high octane product for a given feed input is increased.

In the practice of the invention, it is important to use suificient temperature differential between the adsorption and desorption phases of the segregation cycle to provide a practicable level of selectivity, in terms of octane difference between the aromatics-rich product and the aromatics-lean product. The particular differential will vary with dilferent refinery situations, but in general should be upwards of 100 F. Although selectivity is improved by increasing the temperature diflerential, it is necessary to avoid a temperature in the adsorber which initiates thermal cracking (upwards'of about 700 F.). This imposes a limit on increasing the temperature differential by increasing temperature. The operating pressure is conveniently that imposed from the stabilization tower of the reforming unit, but a pressure suflicient to maintain the reformate in the liquid phase should be employed, at least during adsorption. Although reduction in pressure during the desorption phase of the operating cycle may be beneficial, it is usually impracticable because closer operating control is required, and repressuring may be necessary to pump products to tankage or to recycle. Although silica gel appears to be the most suitable aromatics-selective adsorbent for segregating reformates, the invention does not depend upon a particular property of the adsorbent. There are other known aromatics selective adsorbents, for example, silicic acid, activated alumina, clays such as fullers earth, and magnesium silicates such as Florisil and Magnesol. As noted above the amount of adsorbent is a matter of economics, but it is desirable to use a large enough bed, considering the charge rate to the system, to provide a long enough cycle for flexibility in correlating the temperature switch-point of the feed and the octane or aromatics-content switch-point of the efliuent. The optimum switch-point from low to high temperature input in the adsorption phase approximates the approach to saturation as the octane or aromatics-content of the efliuent passes through a minimum and begins to increase. This may be varied, however, according to relative demand for the high and low octane products.

The reforming operation, according to the invention, may be conducted in the conventional manner. For example, a naphtha feed stock of relatively low octane number, in terms of its blending value in the gasoline pool, such as a virgin or coke still naphtha, may be treated under reforming conditions in the presence of a catalyst and hydrogen. Particularly suitable catalysts are those of the platinum-alumina type, handled in the form of a fixed bed, and molybdena-alumina type catalysts, advantageously handled in the form of a fluidized bed. Typical reforming conditions require a temperature in the range of about 850 to 1000 F., a pressure in the range of about 50 to 750 p.s.i.g. and a recycle hydrogen rate of about 2000 to 10,000 cubic feet per barrel. A space velocity in the range of about 1 to 5 WHSV is usually employed.

We claim:

1. In the production of a plurality of octane grades of gasoline from available refining stocks including reformate, the process which comprises subjecting reformate to a four-phase adsorption cycle which includes saturating a body of solid particle-form adsorbent which is selective for aromatics by flowing a stream of reformate at adsorption temperature through an adsorption zone and collecting an efiluent which is relatively low in octane compared to the reformate feed, purging saturated adsorbent in the adsorption zone by flowing a stream of reformate at an elevated desorption temperature through the zone while collecting an intermediate octane effluent, thereafter effecting desorption of adsorbed aromatics from adsorbent in the adsorption zone by continuing the flow of reformate at elevated desorption temperature through the zone while collecting separately an eflluent which is relatively high in octane compared to the reformate feed, and purging desorbed adsorbent of desorption fluid by flowing a stream of reformate at the adsorption temperature level through the adsorption zone while collecting a second intermediate octane effluent stream.

2. The process of claim 1 in which the adsorbent is silica gel.

3. The process of claim 1 in which the intermediate octane number eflluent streams are combined for blending to finished gasoline.

4. The process of claim 1 in which the adsorption cycle is controlled by measuring the change of aromatics content of the efiluent during each phase of the cycle and in which the change from input of low temperature charge to high temperature charge is timed to anticipate decline of efliucnt octane to the minimum cyclic value and in which the change from high temperature to low temperature input is timed to anticipate rise in the efliuent octane to the maximum cyclic value.

5. In the catalytic reforming of naphtha to produce a product of improved octane value, the method which comprises treating the naphtha charge under reforming conditions in the presence of a catalyst and hydrogen; separating a hydrogen rich gas for recycle from the resulting reformate; subjecting liquid reformate to a fourphase adsorption cycle which includes saturating a body of solid particle-form adsorbent which is selective for aromatics by flowing a stream of reformate at adsorption temperature through an adsorption zone, collecting an efiluent which is relatively low in octane compared to the reformate feed, purging saturated adsorbent in the adsorption zone by flowing a stream of reformate at an elevated desorption temperature through the zone while collecting an intermediate octane efliuent, thereafter effecting desorption of adsorbed aromatics from adsorbent in the adsorption zone by continuing the flow of reformate at elevated desorption temperature through the zone while collecting separately an efliuent relatively high in octane compared to the reformate feed, and purging desorbed adsorbent of desorption fluid by flowing a stream of reformate at the adsorption temperature level through the adsorption zone while collecting a second intermediate octane effluent stream; and recycling the relatively low octane effluent from the adsorption cycle with fresh charge to the reforming step.

6. The method of claim 5 in which the adsorbent is silica gel.

7. The method of claim 5 wherein the desorption temperature level is that of the reformate flowing to the adsorption zone directly from the reforming separation operation and the adsorption temperature level is obtained by cooling reformate flowing to the adsorption zone.

8. The process for producing premium and regular grades of gasoline from a plurality of refinery stocks of relatively high and relatively low octane values which comprises subjecting a naphtha of relatively low octane value to treatment under reforming conditions in the presence of a catalyst and hydrogen; separating a hydrogen rich gas for recycle from the resulting reformate; subjecting liquid reformate to a four-phase adsorption cycle which includes saturating a body of solid particleform adsorbent which is selective for aromatics by flow- 1 ing a stream of reformate at adsorption temperature through an adsorption zone, collecting an efiluent which 9 is relatively low in octane compared to the reformate feed, purging saturated adsorbent in the adsorption zone by flowing a stream of reformate at an elevated desorption temperature through the zone while collecting an intermediate octane eflluent, thereafter effecting desorption of adsorbed aromatics from adsorbent in the adsorption zone by continuing the flow of reformate at elevated desorption temperature through the zone while collecting separately an efliuent relatively high in octane compared to the reformate feed, and purging desorbed adsorbent of desorption fluid by flowing a stream of reformate at the adsorption temperature level through the adsorption zone while collecting a second intermediate octane efliuent stream; blending the relatively high octane efliuent from the adsorption cycle to premium gasoline and combining the intermediate octane effluent streams from. the adsorption cycle for blending to regular gasoline.

9. The pnocess of claim 8 in which the relatively low octane effluent from the adsorption cycle is recycled with fresh charge to the reforming step.

10. The process of claim 8 in which the desorption temperature level is that of the reformate flowing to the adsorption zone directly from the reforming separation operation and the adsorption temperature level is obtained by cooling reformate flowing to the adsorption zone.

11. In the catalytic reforming of naphtha to produce a product of improved octane value, the method which comprises treating the naphtha charge under reforming conditions in the presence of a catalyst and hydrogen; separating a hydrogen rich gas for recycle from the resulting reformate; subjecting liquid reformate to an adsorptiondesorption cycle which includes saturating a body of solid particle form adsorbent which is selective for aromatics by flowing a stream of reformate at adsorption temperature through the adsorption zone, collecting an eflluent which is relatively low in octane compared to the reformate feed, purging saturated adsorbent in the adsorption zone by flowing a stream of reformate at an elevated desorption temperature through the zone While continuing to collect relatively low octane eflluent, thereafter effecting desorption of adsorbed aromatics from adsorbent in the adsorption zone by continuing the flow of reformate at elevated desorption temperature through the zone while collecting separately an eflluent relatively high in octane compared to the reformate feed, and purging desorbed adsorbent of desorption fluid by flowing a stream of reformate at the adsorption temperature level through the adsorption zone While continuing to collect relatively high octane efliuent.

12. The method of claim 11 in which the low octane effluent is recycled with fresh charge to the reforming step.

13. The method of claim 11 in which the adsorbent is silica gel.

14. The method of claim 13 wherein the desorption temperature level is that of the reformate flowing to the adsorption zone directly from the reforming separating operation and the adsorption temperature level is obtained by cooling reforrnate flowing to the adsorption zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,398,101 Lipkin Apr. 9, 1946 2,571,936 Patterson Oct. 16, 1951 2,628,933 Eagle et al. Feb. 17, 1953 2,653,175 Davis Sept. 22, 1953 2,728,716 Watson et al Dec. 27, 1955 2,736,684 Tarnpoll Feb. 28, 1956 FOREIGN PATENTS 1,031,703 France Mar. 25, 1953 OTHER REFERENCES Spengler et al.: Petroleum Rcfiner, July 1952, pp. 111-114. 

1. IN THE PRODUCTION OF A PLURALITY OF OCTANE GRADES OF GASOLINE FROM AVAILABLE REFINING STOCKS INCLUDING REFORMATE, THE PROCESS WHICH COMPRISES SUBJECTING REFORMATE TO A FOUR-PHASE ADSORPTION CYCLE WHICH INCLUDES SATURATING A BODY OF SOLID PARTICLE-FORM ADSORBENT WHICH IS SELECTIVE FOR AROMATICS BY FLOWING A STREAM OF REFORMATE AT ADSORPTION TEMPERATURES THROUGH AN ADSORPTION ZONE AND COLLECTING AN EFFUENT WHICH IS RELATIVELY LOW IN OCTANE COMPARED TO THE REFORMATE FEED, PURGING SATRUATED ADSORBENT IN THE ADSORPTION ZONE BY FLOWING A STREAM OF REFORMATE AT AN ELEVATED DESORPTION TEMPERATURE THROUGH THE ZONE WHILE COLLECTINHG AN INTERMEDIATE OCTANE EFFUENT, THEREAFTER EFFECTING DESORPTION OF ADSORBED AROMATICS FROM ADOSRBENT IN THE ADSORPTION ZONE BY CONTINUING THE FLOW OF REFORMATE AT ELEVATED DESORPTION TEMPERATURE THROUGH THE ZONE WHILE COLLECTING SEPARATELY AN EFFUENT WHICH IS RELATIVELY HIGH IN OCTANE COMPARED TO THE REFFORMATE FEED, AND PURGING DESORBED ADSORBENT OF DESORPTION FLUID FLOWING A STREAM OF REFORMATE AT THE ADSORP- 